Floods of 18 and 19 November 2016 in Batouri (East Cameroon
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Hindawi e Scientific World Journal Volume 2019, Article ID 3814962, 7 pages https://doi.org/10.1155/2019/3814962 Research Article Floods of 18 and 19 November 2016 in Batouri (East Cameroon): Interpretation of the Hydro-Meteorological Parameters and Historical Context of the Post-Event Survey Episode Paulin Sainclair Kouassy Kalédjé ,1 Jules-Rémy Ndam Ngoupayou,1 Alain Fouépé Takounjou,2 Mireille Zebsa,3 Felaniaina Rakotondrabe,4 and Joseph Mvondo Ondoa1 1 Faculty of Science, University of Yaounde1,Yaound´ e-Cameroon,P.O.Box:812Yaound´ e,´ Cameroon 2Hydrological Research Centre, Institute of Geological and Mining Research, Yaounde,´ Cameroon 3Research and Innovation Centre, Ministry of Scientifc Research and Innovation, Bertoua, Cameroon 4Advanced School of Engineering of Antananarivo, University of Antananarivo, Antananarivo, Madagascar Correspondence should be addressed to Paulin Sainclair Kouassy Kaledj´ e;´ [email protected] Received 25 September 2018; Revised 12 November 2018; Accepted 18 November 2018; Published 1 January 2019 Academic Editor: Federico Porcu Copyright © 2019 Paulin Sainclair Kouassy Kaledj´ e´ et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. During the night of November 18 to 19, 2016, many stormy cells are not very mobile organized on the east of the southern plateau of Cameroon and dumped up to 260 mm of rain in 4 hours. Occurring on a relatively saturated soil, these rains caused strong foods of Kadey and Doume.´ Te foods were particularly damaging in the city of Batouri, where a subdivision was submerged by the Boumbe´ (tributary of the Sangha) with water heights in the houses reaching 1.75 m, despite the presence of a dam allowing clipping foods upstream of the basin. In this article, we present the results of the analysis of the postevent survey generated on this event with fow rates estimated on 15 sections of ungauged subbasins. Tese fows are then compared with those obtained from other recent postevent survey and those estimated by various regional estimations. Te inventory of heavy rains around Batouri during the period 1970-2016 has led to the revision of current development standards in the region, which seem to underestimate rainfall and infrequent fows. 1. Introduction exceptional events from the food leashes and the testimony of local residents. Tese operations have notably helped to Te intense rains accompanied by fash foods are one of reevaluate extreme fows in the Mediterranean and tropical 3 2 2 the characteristics of the Equatorial Guinean climate. Te zones, where values greater than 20 m /s/km over a few km extension of urbanized areas in southeastern Cameroon has have frequently been observed [3, 7]. multiplied homes vulnerable to fooding [1–3]. Te collection Te rain that hits the southeast of Cameroon on 18 and of data on fash foods is therefore a crucial issue for the 19 November 2016 had the particularity of reaching in some defnition of food zones and risk control in urban or peri- localities more than 200 mm in 3 hours, with a relatively 2 urban areas. In recent years, the practice of postevent survey small spatial extension, a few hundred km in total, and ofen (REX) has grown considerably in Europe and West Africa [4– only a few dozen square kilometers for the most intense 6] to evaluate fows of these extreme foods. Te purpose of part. Tis phenomenon is not new in the region, but its the REX analysis is to reconstruct the fows achieved during location in urbanized areas has led to very signifcant damage. 2 Te Scientifc World Journal Figure 2: Precipitation casts from November 18, 2016 at 4:00 am GMTto19November2016at6:00amGMT,estimatedfromthe Panthere radar product (lef) and OHM-CV reanalysis (right). Figure 1: Location of the study site and major rivers. BoumbesubbasininKenzouhasthefollowingpercentages´ [11]: scrubland 12%, forests 57%, agricultural land 24%, and urban areas 7%. Kadey has fairly similar percentages, but for Te characteristics of this episode are described in this thetwobasins,theareaafectedbythecumulativehighsis article. Flow rates were estimated a posteriori on eighteen on the immediate periphery of Batouri; the percentage of (18) sections of ungauged rivers. Te values obtained were urbanized area is higher and is around 25%. For the locality compared with those of other recent postevent survey from of Batouri, the percentage of urbanized area is close to 100%. the Southern Cameroon forest. Te return periods of the Te event of November 18 and 19 occurs in a particular episode were qualifed by a regional approach consisting of hydrological context, as two episodes of heavy rainfall hit the inventorying similar episodes that occurred in the vicinity of area the previous month. On October 12th, the stormy rains Batouri during the last 50 years. In addition to this article, mainly afect the south-south sector of the eastern region of information on this phenomenon can also be found in other Cameroon: Bertoua, Mandjou, or Batouri are about 167 mm studies conducted by CEREMA (Center for Studies and and Mbang (south of the city) only 383 mm. Ten, on October Expertise on Risks, the Environment, Mobility and Devel- 25, a new episode touches Batouri with 307 mm in 12 hours opment)(2015)[8],usingthesamefowestimationmethod in Tripano. Te southeast Cameroon receives during this presented here, or by Rey et al. (2016) [9], which describe the episode142mminBertouaand122mminMandjou.On environmental consequences of such a hydrometeorological 18 November, the soils are very humid, the Kadey cracked episode. basins on the sources of Dem and Lom; Kadey has a fow rate 3 of 0.98 m /s, while the low fow rate before 12 October was 3 2. Materials and Methods 0.07 m /s. 2.1. Characterization of the Area. Te area afected by the intense rains of 18 and 19 November 2016 is located in 2.2. Meteorological Event. On November 18, 2017, the rains southeastern Cameroon. Te most impacted villages were started around 9:00 pm (6:00 pm GMT). Te results obtained from west to east: Sandae, Dogbwe, Batouri, Mongonam, from the weather radar images of France show little mobile Mboscoro, Kambel´ e´ III, and Dem (Figure 1). storm cells that have been stationed for about 4 hours in the Te area is drained by two rivers: Kadey in the West and area from Tongo Gadima in the southwest to Tikondi in the Boumbe´ in the East. Kadey has a fairly extensive catchment northeast, about twenty km, whose width does not exceed 7- 2 in the northwest (251 km ) but has had little impact during 8 km. From the analysis of these images, we see that, later in this episode. For the Boumbe,´ the topographic basin at the the night, other cells afected the entire Kadey department, 2 Kenzou station is 109 km . Te hydrogeological catchment, between the locality of Mbang and that of Pana, with lower on a cracked base, feeding the source of the Boumbecovers´ intensities. 2 372 km [10]. Te rapid recharge area of this catchment is Radar images provide an estimate of rainfall and their located north of a ridge and was only slightly afected by the spatial variability (Figure 2). Te Panther radar rain, supplied event. by Met´ eo-France,´ has been corrected for rain gauges using a correction factor, constant in space and updated every hour. Te relief, which is a plateau, consists of small hills, and 2 the altitudes vary between 780 and 1000 meters. Metamor- Te spatial resolution is 1 km and the temporal resolution phic rocks are largely in the majority but this sector has is 5 mm. Te radar rain OHM-CV (Mediterranean Hydrom- some karstic outcrops, the latter being located more to the eteorological Observatory Cevennes-Vivarais)´ corresponds northwest. Land use is made up of scrubland, areas, and to a reanalysis with a variable correction factor in space, 2 urbanized areas dominated by forest and mining structures interpolated by kriging. Te spatial resolution is 1 km and that have been expanding rapidly in recent decades. Te the reanalysis is available at a time resolution of 60 minutes. Te Scientifc World Journal 3 120 300 100 250 80 200 60 150 40 100 20 50 0 0 Figure 3: Equipment of the station of Kadey with Batouri in 6h4h2h24h22h20h18h16h14h12h10h8h6h automatic station. Hourly rains Cumulated rains Te images difer between Batouri and Kenzou, a sector where Panther totals are underestimated compared to OHM- Figure 4: Hyetogram of the rain at the pixel that provided the CV totals. According to the OHM-CV reanalysis, the accu- maximum rain, at Batouri, from 18 November at 6:00 am GMT to mulations are of the order of 280 mm in the commune of 19 November at 6:00 am GMT. Batouri and 265 mm in the commune of Kenzou. According to this same treatment, the areas corresponding to rainfall 3 2 totals greater than 100, 150, and 200 mm are, respectively, specifc discharge is 5.6 m /s/km for a catchment with an 2 2 264, 123, and 67 km . Te OHM-CV radar rains are closer area of 102 km . Several testimonies concerning the water to the ground-based rainfall than the Panther radar rains, levelsontheroadindicateneverthelessthatthefoodofMay particularly in Mandjou and Kenzou. It is the consequence 12, 2001, was as important as that of November 19, 2016, at the confuence Boumbe-Kadey.´ of the treatment that spatially interpolates the diference 3 Furtherdownstream,thefoodreaches499m/s at between radar rain and values of the rains obtained by 2 Kambel´ e´ III on Boumbe,´ for a catchment area of 115 km , pluviometers on the level of the ground (Figure 3), while 3 2 the correction of radar rain is spatially uniform in the case i.e., a specifc fow of 4.3 m /s/km .